A vehicle transmission system is equipped with a pump to supply fluid to power vehicle clutches as well as to provide lubrication and cooling to the transmission systems. The vehicle engine provides power to a pump in many previous pumping systems and, thus, the systems are only operable when the engine is running. In these previous systems, there is no mechanical ability to run the hydraulic pump when the engine is not running. However, situations exist where the engine is off but vehicle mechanisms are in motion, such as when a battery powers an electric/gasoline hybrid vehicle. Another previous method to provide pumping when the engine is not running is to include a separate pump for each power source rather than a single pump operable by multiple power sources. For example, in a multi-pump system for a hybrid gasoline/electric vehicle, when the engine is running, a first pump operates to drive fluid through the system and a second pump is inoperable, but when the vehicle is electrically powered the first pump is inoperable and the second pump operates. This solution, however, requires more packaging space than a conventional one-pump system because of the additional pump or pumps required. There is a need for a vehicle pumping system that operates both when the engine is running and when the vehicle is powered by other power sources, such as an electric battery or electric motor, while also maintaining or improving the system packaging requirements.
An electromechanical transmission is described in commonly assigned U.S. patent application Ser. No. 11/071,406 entitled “Electrically Variable Transmission with Selective Fixed Ratio Operation,” Holmes et al., filed Mar. 3, 2005 and is hereby incorporated by reference in its entirety.